Method and apparatus for riding through power disruptions of a drive circuit

ABSTRACT

An electrical ride-through (ERT) unit is configured to apply a voltage to a drive circuit during disruptions of line voltage to the drive circuit. The ERT unit includes a capacitor on an ERT circuit that is prevented from applying the voltage to the drive circuit during normal operation of the drive circuit, and applies the voltage to the drive circuit during a voltage drop on the drive circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 17/090,100filed Nov. 5, 2020, the disclosure of which is hereby incorporated byreference as if set forth in its entirety herein.

BACKGROUND

Electrical drives often draw electrical power from the electrical gridof the local electric utility or power supplier to drive any electricaldevice as desired. Some applications achieve benefits when theelectrical drive is configured as a variable speed drive (VSD),including electrical submersible pumps (ESP) and salt water disposal(SWD) among other industrial applications.

Disruptions in line voltage to the drive can cause the electricallypowered device to cease operation. This decreases production efficiency,and also requires the pump to be restarted which is often difficult. Forinstance, when an ESP is shut down, sand and other sediment canaccumulate in the downhole pump which can get stuck, thereby increasingthe difficulty of restarting the ESP. Disruptions in the line voltagecan be in the form of a power outage or a voltage sag. Voltage stopsoccur when voltage is no longer delivered to the drive. When voltagesags occur, the DC bus voltage on the drive will oscillate, which thecontroller can interpret as a phase loss in the input line, anddiscontinue operation of the pump. Further, the drive can also include acontrol power transformer that receives line voltage and powersauxiliary electrical components of the drive, such as the controller andcontactors, and the like. A voltage sag or voltage stop on one of thelines to the control power transformer can cause a decreased voltagesupply to the control power transformer, which can cause the controllerto shut down the pump.

A need currently exists for a system that reliably provides electricalpower to drives that are used to control a load, such as an ESP or othersuitable device as desired, during disruptions in the electrical powersupply to the drive.

SUMMARY

In one aspect of the present disclosure, an electrical ride-through(ERT) unit is configured to apply a voltage to a drive system during adisruption of line voltage input to the drive circuit. The ERT unit caninclude an energy storage section connected between positive andnegative lines of an ERT circuit, the storage section configured toselectively store and discharge energy. The ERT unit can also include anoutput diode on the positive line of the ERT circuit, wherein thepositive line is configured to connect to a positive line of a drivecircuit of the drive system, such that the diode is disposed between thestorage section and the positive line of drive circuit. The output diodecan be configured to prevent electrical current from flowing from thestorage section to the drive circuit when a voltage level on the drivecircuit is greater than the voltage level of the storage section. Theoutput diode can be configured to permit current to flow from thestorage section to the drive circuit when the voltage level on the drivecircuit is less than the voltage level of the storage section.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofillustrative embodiments of the intervertebral implant of the presentapplication, will be better understood when read in conjunction with theappended drawings. For the purposes of examples of the presentdisclosure, there is shown in the drawings illustrative embodiments. Itshould be understood, however, that the application is not limited tothe precise arrangements and instrumentalities shown. In the drawings:

FIG. 1 is a circuit schematic diagram of a conventional variable speeddrive that controls electrical power to a load, such as an ESP;

FIG. 2 is a circuit schematic diagram of an electrical ride through unitconfigured to deliver electrical power to a load during periods ofdisruption in the electrical power supply to the load; and

FIG. 3 is a circuit schematic diagram of an electrical control systemincluding the electrical ride through unit of the type illustrated inFIG. 2 integrated into a variable speed drive of the type illustrated inFIG. 1 ;

FIG. 4A is a flowchart showing steps associated with operation of theelectrical ride-through unit in one example;

FIG. 4B is a flowchart showing steps associated with a charging mode ofthe electrical ride-through unit;

FIG. 4C is a flowchart showing steps associated with a ride-through modeof the electrical ride-through unit; and

FIG. 4D is a flowchart showing steps associated with a discharge mode ofthe electrical ride-through unit.

DETAILED DESCRIPTION

The present disclosure can be understood more readily by reference tothe following detailed description taken in connection with theaccompanying figures and examples, which form a part of this disclosure.It is to be understood that this disclosure is not limited to thespecific devices, methods, applications, conditions or parametersdescribed and/or shown herein, and that the terminology used herein isfor the purpose of describing particular embodiments by way of exampleonly and is not intended to be limiting of the scope of the presentdisclosure. Also, as used in the specification including the appendedclaims, the singular forms “a,” “an,” and “the” include “at least one”and a plurality. Further, reference to a plurality as used in thespecification including the appended claims includes the singular “a,”“an,” “one,” and “the,” and further includes “at least one.” Furtherstill, reference to a particular numerical value in the specificationincluding the appended claims includes at least that particular value,unless the context clearly dictates otherwise.

The term “plurality”, as used herein, means more than one. When a rangeof values is expressed, another example includes from the one particularvalue and/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another example. Allranges are inclusive and combinable.

The term “substantially,” “approximately,” and derivatives thereof, andwords of similar import, when used to described sizes, shapes, spatialrelationships, distances, directions, and other similar parametersincludes the stated parameter in addition to a range up to 10% more andup to 10% less than the stated parameter, including up to 5% more and upto 5% less, including up to 3% more and up to 3% less, including up to1% more and up to 1% less.

Referring to FIG. 1 , a variable speed drive (VSD) system 20 can includea load 22 and a VSD circuit 24 that is configured to condition inputelectrical power, and deliver power to a motor of the load 22. In oneexample, the load 22 can be configured as a motor of an electricallypowered device. The electrically powered device can be a device thatundergoes reciprocating or rotatable motion, such as a submersible pumpjack, though the electrically powered device can undergo any motion asdesired. It should be recognized, of course, that the load 22 can bealternatively configured as desired. Aspects of the present disclosurehave particular applicability to loads that are susceptible to timelyand costly restarts in response to ride-through events such as momentarydisruptions in the power supply (either due to a voltage stop or avoltage sag in the line voltage to the VSD circuit 24) and the like.

The VSD circuit 24 includes a common VSD DC bus 29 having a positiveline 29 a and a negative line 29 b, a VSD alternating current (AC) todirect current (DC) converter section 26 on the DC bus 29, a VSD storagesection 27 on the DC bus 29, and a VSD inverter section 28 on the DC bus29. The load 22 receives electrical power from a three-line output ofthe VSD inverter section 28. The DC bus 29 thus places the convertersection 26, the VSD storage section 27, and the VSD inverter section 28in electrical communication with each other. In one example, the VSDstorage section 27 and the inverter section 28 can be connected inseries with the VSD converter section 26. The VSD converter section 26is configured to receive 3-phase electrical power along three respectivelines (also referred to herein as line voltage) from any suitable powersource 25. The power source 25 can be provided as the electrical powergrid, or any suitable alternative power source as desired. The inputline voltage can be a typical 480 volt (V) three phase input, inparticular when the power source 25 is defined by the electrical powergrid. In one example, the converter section 26 can include a pluralityof diodes 30 that are arranged as pairs of diodes that are connectedbetween the positive and negative lines 29 a-b of the DC bus 29, suchthat the pairs are connected in parallel with each other. The diodes 30of each pair of diodes can include first and second diodes 30 that areconnected in series with each other between the positive and negativelines 29 a and 29 b. The diodes 30 of each pair of diodes are forwardbiased in the same direction from the positive line 29 a to the negativeline 29 b. The AC to DC converter section 26 can include three pairs 32a, 32 b, and 32 c of diodes 30. Each of the pairs 32 a, 32 b, and 32 care connected in parallel. Further, the diodes 30 of each of the pairs32 a, 32 b, and 32 c are forward biased in the same direction. Each ofthe pairs 32 a, 32 b, and 32 c is connected to a respective one line,and thus a respective one phase, of the 3-phase input. In this manner,the diodes 30 are arranged as a diode bridge 34 that rectifies thevoltage received from the AC power source 25, and outputs a single phaseDC bus voltage to the DC bus 29.

The VSD storage section 27 can further include a VSD capacitor bank 36that is connected to the DC bus 29 from the positive line 29 a to thenegative line 29 in parallel with the VSD converter section 26. The VSDcapacitor bank 36 is configured to receive and store the single-phase DCbus voltage output from the VSD converter section 26. The VSD capacitorbank 36 can be provided as a single DC capacitor or a plurality of DCcapacitors as desired. The single-phase DC bus voltage from the VSDconverter section 26 charges the VSD capacitor bank 36 to a desiredvoltage. The VSD capacitor bank 36 can have any suitable capacitance asdesired. In one example, the capacitance is in a range fromapproximately 10,000 microfarad (mfd) to approximately 30,000 mfd. Ingeneral, the capacitance is related to the peak current that is to besupplied to the motor of the load 22. In particular, the voltage on theVSD capacitor bank 36 can power the inverter section 28. Of course thegreater the load current to be supplied to the load 22, the more energyis to be stored in the VSD capacitor bank 26, and applied to theinverter section 28 over the DC bus 29.

The inverter section 28 receives the DC bus voltage from the DC busvoltage and generates AC output waveforms received by the load 22. Inone example, the inverter section 28 can include a plurality ofinverters 38 that are arranged as pairs of inverters, wherein the pairsare connected in parallel with each other. The inverters 38 of each pairof inverters can include first and second diodes inverters 38 that areconnected in series with each other. The inverter section 28 can includethree pairs 40 a, 40 b, and 40 c of inverters 38. Each of the pairs 40a, 40 b, and 40 c are connected in parallel. Each of the pairs 40 a, 40b, and 40 c of inverters 38 is electrically connected along a separateline to the load 22.

The variable speed drive (VSD) system 20 can also include auxiliaryelectrical components as desired, such as a controller, display, faultcircuitry, contactors, and the like as is understood by one havingordinary skill in the art. The VSD circuit 24 further includes a controlpower transformer (CPT) 42 that is configured to deliver electricalpower to one or more up to all of the auxiliary electrical components.The CPT 42 is electrically connected to two of the three lines of the3-phase electrical power source 25. Thus, in one example, single-phaseelectrical power is input to the CPT 42 at the voltage and frequency ofthe electrical power source, that is 480V at 60 Hz. It is recognizedthat the VSD system 20 can include any number of CPTs 42 as desired. TheCPT 42 can be configured as a step-down transformer creates that reducesthe voltage with respect to the input voltage, so as to output lowvoltage that drives the auxiliary electrical components. While the CPT42 can be configured to receive a 480V input, and output 120V in oneexample, it is recognized that the CPT 42 can be configured to outputany voltage as desired dependent upon the design of the variable speeddrive system 20. By way of example and not limitation, the outputvoltage of the CPT 42 can be in a range from approximately 50V toapproximately 300V.

While the VSD system 20 is illustrated as including a single CPT 42, itis recognized that the VSD system 20 can include any number of CPTs 42as desired, such as at least one or more CPTs 42. Each CPT 42 can beconfigured to supply electrical power to a dedicated one or moreelectrical components. Each CPT 42 can receive input line voltage fromthe electrical power source 25 or from its own power source.

It is recognized that a ride-through event can disable the VSD system20. In particular, the CPT can lose electrical power, and after the VSDcapacitor bank 36 has been discharged which disrupts electrical power tothe load 22. This results in disruptions in operation of the load 22,and requires valuable time to restart the load once the input electricalpower is resumed. Further, as described above, restarting submersiblepumps can create a risk of damaging the pump.

Referring now to FIGS. 1 and 2 , an electrical ride-through (ERT) unit44 can be configured to supply sufficient electrical power to continueoperation of the load 22, and can further be configured to provideelectrical power to the CPT 42 in order to maintain operation of the CPT42 and the electrical components that are powered by the CPT 42. Inparticular, as will now be described the ERT unit 44 can includechargeable circuitry that is configured to deliver electrical power tothe VSD circuit 24 during periods of interruption in the electricalpower source 25.

With continuing reference to FIG. 2 , the ERT unit 44 can include an ERTcircuit 45 that includes an ERT DC bus 49, and a ride-through (ERT) ACto DC converter section 46, an ERT storage section 48, and an ERT outputsection 50 on the ERT DC bus 49. The ERT converter section 46 isconfigured to receive input AC electrical power and convert thealternating current to direct current. The ERT storage section 48 isconfigured to store power that is to be output to the VSD circuit 24during disruptions in the input line voltage to the VSD circuit 24. TheERT output section 50 is configured to allow current to flow from theride-through storage section 48 to the VSD circuit 24 during instancesof disruptions in the input line voltage to the VSD circuit 24, andprevent current from flowing from the ride-through energy storagesection 48 to the VSD circuit 24 during normal operation (i.e., when theinput line is delivering the three-phase 480 V at 60 Hz to the VSDcircuit 24, and in particular to the VSD converter section 26). The ERTconverter section 46, the ERT storage section 48, and the ERT outputsection 50 will now be described in more detail.

The ERT converter section 46 can be constructed as described above withrespect to the VSD converter section 26, and thus can be configured as aplurality of diode bridges that are connected in parallel with eachother between a positive line 49 a of the ERT DC bus 49 and a negativeline 49 b of the ERT DC bus 49. Each of the diode bridges receive avoltage input from a respective one of the phases of input line voltage.Thus, the ERT converter section 46 is configured to receive a 3-phaseelectrical input line voltage from any suitable power source 47, such asthe electrical power grid, rectify the AC line voltage, and output asingle-phase DC bus voltage to the ERT DC bus 49. The line voltage canbe a typical 480 volt (V) three phase input at 60 Hz.

The ERT storage section 48 is on the ERT DC bus 49, and can be connectedin parallel with the ERT converter section 46 between the positive line49 a and the negative line 49 b. The ERT storage section 48 can includean ERT capacitor bank 52 that is configured to receive and store thesingle-phase DC bus voltage output from the ERT converter section 46.The ERT capacitor bank 52 can be provided as a single DC capacitor or aplurality of DC capacitors as desired. The single phase DC bus voltageoutput by the ERT converter section 46 onto the ERT DC bus 49 chargesthe ERT capacitor bank 52 to a desired voltage.

The ERT capacitor bank 52 can have any suitable capacitance as desired.In one example, the capacitance of the ERT capacitor bank 52 is greaterthan the capacitance of the VSD capacitor bank 36. In particular, thecapacitance of the ERT capacitor bank 52 is designed to deliversufficient energy to the VSD circuit 24 over a predetermined duration oftime that is deemed suitable to power the drive 20 during momentarypower outages in the line voltage input to the VSD circuit 24. In oneexample, the ERT capacitor bank 52 can have at least one or moresupercapacitors. By way of example and not limitation, the ERT capacitorbank 52 can have a capacitance in a range from than approximately 1Farad (F) to approximately 50 F. In one particular example, thecapacitance of the ERT capacitor bank 52 can be approximately 11 F.

Referring now also to FIG. 3 , an electrical drive system 21 can includethe VSD system 20 and the ERT unit 44 integrated into the VSD system.For instance, the ERT circuit 56 can be integrated into the VSD circuit.In one example, the ERT output section 50 can be configured to allowcurrent to flow from the ERT capacitor bank 52 to the VSD DC bus 29 onlyduring a disruption of the line voltage to the VSD DC bus 29. In oneexample, the output section 50 includes at least one ERT output diode 54on the positive line 49 a that is forward biased toward the positiveline 29 a of the VSD DC bus 29. The positive line 49 a of the ERT DC bus49 is connected from the ERT output diode 54 to the positive line 29 aof the VSD DC bus 29. The negative line 49 b of the ERT DC bus 49 isconnected to the negative line 29 b of the VSD DC bus 29.

When the voltage on the VSD DC bus 29 is greater than the voltage of thecharged ERT capacitor bank 52, as is the case during normal operation,the ERT output diode 54 is configured to prevent the ERT capacitor bank52 from conducting. When the voltage on the VSD DC bus 29 is less thanthe voltage of the charged ERT capacitor bank 52, as is the case duringan interruption of voltage on the line input to the VSD DC bus 29, theERT output diode 54 is configured to allow the ERT capacitor bank 52 toconduct to the positive line 29 a of the VSD DC bus 29.

With continuing reference to FIG. 3 , the ERT unit 44 can furtherinclude a controller 56 that governs the operation of the ERT circuit45. For instance, the ERT circuit 45 includes a first charging contactor58 a on the positive line 49 a of the ERT DC bus 49 between the ERTconverter section 46 and the ERT storage section 48, and a secondcharging contactor 58 b on the negative line 49 b of the ERT DC bus 49between the ERT converter section 46 and the ERT storage section 48.When the charging contactors 58 a and 58 b are closed, the ERT capacitorbank 52 is placed in electrical communication with the ERT convertersection 46. When the charging contactors 58 a and 58 b are open, the ERTcapacitor bank 52 is electrically decoupled from the ERT convertersection 46.

The ERT circuit 45 includes an output contactor 60 on the positive line49 a of the ERT DC bus downstream of the ERT output diode 54 withrespect to the direction of current flow. The output contactor 60 isfurther electrically connected to the positive line 29 a of the VSD DCbus 29 at a location between the VSD capacitor bank 36 and the VSDinverters 38. When the output contactor 60 is closed, the cathode sideof the ERT capacitor bank 52 is electrically connected to the inverters38. When the output contactor 60 is open, the cathode side of the ERTcapacitor bank 52 is electrically decoupled from the VSD DC bus 29, andin particular the inverters 38.

The ERT circuit 45 further includes a discharge contactor 62electrically connected between the positive line 49 a and the negativeline 49 b of the ERT DC bus 49. The discharge contactor 62 is thusconnected in parallel with the ERT capacitor bank 52. The ERT circuit 45further includes a resistor 64 on the positive line 49 a of the ERT DCbus 49 between the discharge contactor 62 and the ERT capacitor bank 52.

The controller 56 is configured to control the first and second chargingcontactors 58 a and 58 b, the output contactor 60, and the dischargecontactor 62 so as to iterate the ERT circuit 45, and thus the ERT unit44, between a charging mode, a ride-through mode, and a discharge mode.The charging mode, the ride-through mode, and the discharge mode willnow be described in more detail.

With continuing reference to FIG. 3 , the ERT circuit 45, and thus theERT unit 44, is in charging mode when the charging contactors 58 a and58 b are closed. The ERT circuit 45, and thus the ERT unit 44, exitcharging mode when the charging contactors 58 a and 58 b are open. Thus,the ERT circuit is configured to selectively couple the ERT storagesection 48 to the ERT converter section 46 during the charging mode, anddecouple the ERT storage section 48 from the ERT converter section 46when charging of the ERT storage section 48 is completed. When the ERTunit 44 is in the charging mode, the single-phase DC voltage on the ERTDC bus 49 is delivered to the ERT capacitor bank 52, thereby chargingthe ERT capacitor bank 52. Further, the output contactor 60 and thedischarge contactor 62 can both be open during charging mode. When thecharging mode has been completed, electrical power is no longerdelivered from the ERT converter section 46 to the ERT storage section48.

The ERT capacitor bank 52 is charged substantially to a target voltagethat is no greater than the voltage on the VSD DC bus 29 that is appliedto the load 22 during normal operation (also referred to as operatingvoltage). For instance, the target voltage can be no greater than, suchas less than, the operating voltage of the VSD DC bus 29, but sufficientto continue operation of the load 22 during voltage disruptions on theVSD DC bus 29. In one example, the target voltage can be in a range fromapproximately 50% of the operating voltage of the VSD DC bus 29 toapproximately 99% of the operating voltage of the VSD DC bus 29. Forinstance, the target voltage can be in a range from approximately 80% ofthe operating voltage of the VSD DC bus 29 to approximately 99% of theoperating voltage of the VSD DC bus 29. In particular, the targetvoltage can be approximately 95% of the operating voltage of the VSD DCbus 29. The resistor 64 can limit peak charging current during chargingof the ERT capacitor bank 52. The resistor 64 can have any suitableresistance as desired, sufficient to charge the ERT capacitor bank 52 ina suitable amount of time while maintaining the maximum current on theERT DC bus 49 as desired. For instance, in some instances, it may bedesirable to limit the peak charging current to approximately 20 A orless. In one example, the resistance of the resistor 64 can be in arange from approximately 6 ohms to approximately 15 ohms. It isappreciated, of course, that the peak charging current and theresistance of the resistor 64 are design variables that can be adjustedas desired.

After the ERT capacitor bank 52 has substantially reached the targetvoltage, the ERT circuit 45 can discontinue charging mode by opening thefirst and second charging contactors 58 a-58 b. The controller 56 closesthe ride-through contactor 60 to enter ride-through mode. The chargingcontactors 58 a and 58 b and the discharge contactor 62 can be openduring ride-through mode. In ride-through mode, the cathode of the ERTcapacitor bank 52 is electrically connected to the positive side of theVSD inverters 38 through the closed ride-through contactor 60. Becausethe voltage on the VSD DC bus 29 during normal operation is greater thanthe voltage of the charged ERT capacitor bank 52, the ERT output diode54 is not electrically conductive, which prevents the ERT capacitor bank52 from conducting energy to the VSD DC bus 29.

However, when an electrical power disruption occurs on the line voltageinput to the VSD circuit 24, the VSD capacitor bank 36 discharges, andthe voltage on the VSD DC bus 29 falls to a level below the voltage ofthe charged ERT capacitor bank 52. As a result, the ERT output diode 54becomes electrically conductive, and current flows from the ERT outputdiode 54 through the ERT output diode 54 to the positive line 29 a ofthe VSD DC bus 29, and thus to the VSD inverters 38. The inverters 38then apply electrical power to the load 22 in the manner describedabove. Because the voltage supplied to the load 22 does approach zerodue to the voltage supply from the ERT capacitor bank 52, the load 22does not discontinue operation in response to the disruption of inputvoltage. It is further recognized that the voltage applied to the load22 from the ERT capacitor bank 52 is less than the voltage applied tothe load 22 during normal operation, the load 22 may not operate at fullcapacity. However, because the target voltage of the ERT capacitor bank52 is only slightly less than the voltage applied to the load 22 duringnormal operation, the load 22 can operate at levels close to fullcapacity. Further, because the load 22 does not shut down, it does notrequire restarting upon resumption of the line voltage input to the VSDcircuit 24.

Once the disruption to the line voltage input to the VSD circuit 24 hasended and normal operation has resumed, the voltage on the VSD DC bus 29increases to a level greater than the voltage applied to the DC bus 29from the ERT capacitor bank 52. As a result, the ERT output diode 54becomes electrically nonconductive, and electrical current no longerflows from the ERT capacitor bank 52 to the VSD circuit 24. The ERTcircuit 45 can then enter charging mode to once again charge the ERTcapacitor bank 52 to the target voltage. It is expected that thecapacitance of the ERT capacitor bank 52 is sufficient to drive the VSDcircuit 24 for a period of time that is sufficient to endure periods ofdisruptions to the power supply to the VSD circuit 24. In this regard,the ERT capacitor bank 52 can have any suitable capacitance as desired,that is deemed suitable to allow the load 22 to ride through disruptionsin the power supply of the VSD circuit 24.

With continuing reference to FIG. 3 , the discharge mode allows the ERTcapacitor bank 52 to discharge its stored energy, for instance when theVSD system 20 is not in operation. When the discharge contactor 62 isclosed and the charging contactors 58 a and 58 b are open, the ERT unitis in discharge mode. During discharge mode, the ERT DC bus 49 defines aclosed loop that includes the ERT capacitor bank 52 and the resistor 64connected in series with the ERT capacitor bank 52, thereby allowing theERT capacitor bank 52 to discharge its stored energy. The resistor 64can limit the electrical current as the ERT capacitor bank isdischarged. The output contactor 60 can also be open in discharge modeto electrically decouple the ERT capacitor bank 52 from the VSD circuit24 while the energy from the ERT capacitor bank 52 discharges its storedenergy.

Any of the contactors 58 a-58 b, 60, and 62 can be normally open ornormally closed as desired. In one example, electrically ride-throughcircuit 45 is normally in discharge mode. Thus, the charging contactors58 a and 58 b and the output contactor 60 are normally open to decouplethe ERT capacitor bank 52 from the ERT converter section 46 and the VSDcircuit 24, and the discharge contactor 62 is normally closed so thatthe ERT capacitor bank 52 discharges its stored energy. When thedischarge contactor 62 is open, the discharge contactor prevents thecapacitor bank 52 from discharging its stored energy on the ERT circuit45. The ERT capacitor bank 52 is therefore only able to discharge itsstored energy when it applies a voltage onto the VSD DC bus 29.

With continuing reference to FIG. 3 , the ERT circuit 45 can include anelectrical generator 66 that receives single-phase line voltage from arespective electrical power source, which can be defined by the powersource 47 that drives the ERT circuit 45, or its own dedicatedelectrical power source. The electrical generator 66 can be configuredto receive, and output, single-phase electrical power at 480V at 60 Hz.Thus, during periods of electrical power disruption, the CPT 42 isdriven by the electrical power received from the electrical generator66. Accordingly, the CPT can output the voltage that drives theauxiliary electrical components in the manner described above. Duringnormal operation, the CPT 42 can receive line input through thegenerator 66.

Thus, the ERT unit 44, and in particular the electrical generator 66,can supply electrical power to the CPT 42 to maintain operation of theCPT 42 during periods of disruption in the line voltage input to the VSDcircuit 24. It is appreciated that any suitable alternative electricaldevice can be supply electrical power to the CPT 42 as desired. Otherembodiments are envisioned to provide electrical power to the auxiliaryelectrical components of the VSD system 20. For instance, the ERT unit44, and in particular the generator 66 or alternative device, canalternatively supply electrical power directly to the auxiliaryelectrical components during a disruption in line voltage input to theVSD circuit 24. Of course, it may be desirable to disconnect the CPT 42from the three-phase input during periods of disruption in the linevoltage to prevent voltage spikes to the auxiliary electrical componentswhen the disruption in line voltage has ended. Thus, a contactor can beopened and closed as desired to control the connection from the linevoltage to the CPT 42. Whether the generator 66 supplies power to theCPT 42 or directly to the auxiliary electrical components, it can besaid that the generator supplies voltage that powers the auxiliaryelectrical components.

Operation of the ERT unit 44 will now be described with referencegenerally to FIGS. 3-4D. Operation of the ERT unit 44 can be performedby the controller 56, which can be defined by one or more components,including sensors, or the like that operate a stored program in volatileor non-volatile memory. It should be appreciated that while FIGS. 4A-4Dshow certain steps associated with various modes of operation, thepresent disclosure is not limited to the steps illustrated, nor is thepresent disclosure limited to performing all of the steps illustrated.Further, it is recognized that some of the steps can be performed in adifferent order than the order illustrated.

Referring initially to FIGS. 3 and 4A, a method 67 for operating the ERTunit 44 can be initiated at a starting step 68, whereby the controller56 is activated. The ERT circuit 45 can initially be in discharge modeupon initiation of the controller, due to the normally open chargingcontactors 58 a and 58 b and output contactor 60, and normally closeddischarge contactor 62. The controller begins at step 68 by initiatingcharging mode 70 at step 69.

In particular, referring to FIG. 3 and FIGS. 4A-4B, when the ERT circuit45 enters charging mode 70, the controller 56 opens the dischargecontactor 62 at step 72 if the discharge contactor 62 is closed. If thedischarge contactor 62 is normally open, then the controller 56 ensuresthat the discharge contactor 62 is open at step 72. Next, at step 74,the controller 56 ensures that the output contactor 60 is open. If theoutput contactor 60 is closed, the controller 56 opens the outputcontactor 60 at step 74. At step 76, the controller 56 closes thecharging contactor 62. If the charging contactor 62 was already open,then the controller 56 ensures that the charging contactor 62 is closed.At decision block 78, the controller determines whether the ERTcapacitor bank 52 has been charged to its capacity at the targetvoltage. If not, the charging contactor 62 remains closed until it isdetermined that the ERT capacitor bank 52 has been charged to itscapacity approximately at the target voltage, at which point thecontroller 56 iterates the ERT circuit 45 to ride-through mode at step80.

Referring now to FIGS. 3, 4A, and 4C, ride-through mode 82 begins atstep 84, whereby the controller 56 opens the charging contactors 58 a-58b. Alternatively, if the charging contactors 58 a-58 b were alreadyopen, then the controller 56 ensures that the charging contactors 58a-58 b are open at step 84. Next, at step 86, the controller 56 ensuresthat the discharge contactor 62 is open. Alternatively, if the dischargecontactor 62 is closed, then the controller 56 opens the dischargecontactor 62 at step 86. Next, at step 88, the controller closes theoutput contactor 60. Alternatively, if the output contactor 60 wasalready closed, then the controller 56 ensures that the output contactor60 is closed at step 88.

It is recognized the VSD circuit 24 may undergo periods of line voltagedisruption while the ERT capacitor bank 52 is in ride-through mode 82.The controller 56 can further operate the generator 66 to supply powerto the CPT 42 when a power outage is sensed. By way of example, thepower outage can be sensed by dissipation of the energy stored in theERT capacitor bank 52, or can be sensed at the electrical power grid. Itis further recognized that the ERT capacitor bank can dissipate energyduring the ride-through mode 82. For instance, when the VSD circuit 24experiences a power disruption, the ERT capacitor bank 52 applies avoltage to the VSD circuit 24 in the manner described above to continueoperation of the load 22. This causes the energy stored in the ERTcapacitor bank 52 to fall. Further, the ERT capacitor bank 52 can supplypower to the controller 56 and other electrically powered components ofthe ERT unit 44. In particular, the ERT circuit 45 can include a DC toDC converter that uses energy stored in the ERT capacitor bank 52 toprovide voltage levels that drive the controller and other electricallypowered components of the ERT unit 44. This can also cause the energystored in the ERT capacitor bank 52 to fall. In another example, the ERTcapacitor bank 52 can slowly discharge over time during normaloperation, which causes its stored energy to fall. Once the storedenergy in the ERT capacitor bank 52 has fallen to a threshold level thatwarrants recharging of the ERT capacitor bank 52, the ERT controller 56can iterate the ride-through circuit 45 to charging mode 70 (see FIG.4B) at step 90 in the manner described above after the electrical powerinput has been restored to the VSD circuit 24.

At step 92 shown in FIG. 4A, the controller 56 can iterate the ERTcircuit to discharge mode 94, as will be now be described with referenceto FIGS. 3, 4A, and 4D. In particular, it may be desired to dischargethe ERT capacitor bank 52 when shutting down the ERT unit 44.Alternatively it may be desirable to discharge the ERT capacitor bank 52when performing maintenance. Discharge mode 94 begins at step 96 wherebythe controller 56 ensures that the charging contactors 58 a and 58 b areopen. If the charging contactors 58 a and 58 b were closed, thecontroller 56 opens the charging contactors 58 a and 58 b at step 96.Next, at step 98, the controller 56 opens the output contactor 60.Alternatively, if the output contactor 60 was already open, then thecontroller 56 ensures that the output contactor 60 is open at step 98.Next, at step 100, the controller 56 closes the discharge contactor 62.Alternatively, if the discharge contactor 62 was already closed, thenthe controller ensures that the discharge contactor 62 is closed. Oncethe ERT capacitor bank 52 has been discharged, maintenance can beperformed or operation of the ERT unit 44 can be discontinued at shutdown step 102.

It should be understood that the foregoing description is onlyillustrative of the present invention. Various alternatives andmodifications can be devised by those skilled in the art withoutdeparting from the present invention. Accordingly, the present inventionis intended to embrace all such alternatives, modifications, andvariances that fall within the scope of the appended claims.

What is claimed is:
 1. An electrical ride-through (ERT) unit configuredto apply a voltage energy to a drive system during a disruption of linevoltage input to a drive circuit of the drive system, the ERT unitcomprising: an ERT circuit having a positive line and a negative line,the ERT circuit in a first condition being configured to selectivelycouple the positive line of the ERT circuit with a positive line of thedrive circuit, the ERT circuit in a second condition being configured toselectively decouple the positive lines of the ERT circuit and the drivecircuit; an energy storage section connected between the positive andnegative lines of the ERT circuit, the energy storage section configuredto selectively store and discharge energy; and an output diode disposedon the positive line of the ERT circuit, wherein in response to the ERTcircuit in the first condition having the positive line of the ERTcircuit coupled to the positive line of the drive circuit, the outputdiode is: disposed in electrical connection between the energy storagesection and the positive line of the drive circuit, configured toprevent electrical current from flowing when a voltage level on thedrive circuit is greater than a voltage level of the energy storagesection, and configured to permit electrical current to flow when thevoltage level on the drive circuit is less than the voltage level of theenergy storage section.
 2. The ERT unit of claim 1, wherein the energystorage section comprises a capacitor having a capacity greater thanapproximately 1 Farad.
 3. The ERT unit of claim 1, further comprising anelectrical generator that is configured to supply voltage that powersauxiliary electrical components of the drive system.
 4. The ERT unit ofclaim 3, wherein the electrical generator is configured to supplyvoltage to a control power transformer of the drive system.
 5. The ERTunit of claim 1, further comprising an output contactor disposed on thepositive line of the ERT circuit, wherein the output diode is disposedbetween the output contactor and the positive line of the drive circuitof the drive system.
 6. The ERT unit of claim 1, further comprising anoutput contactor disposed on the positive line of the ERT circuit, theoutput contactor configured to iterate between: an open state for theERT circuit in the second condition, whereby the energy storage sectionis electrically disconnected from the drive circuit of the drive system;and a closed state for the ERT circuit in the first condition, wherebythe energy storage section is configured to be placed in electricalcommunication with the drive circuit of the drive system through theoutput diode.
 7. The ERT unit of claim 6, further comprising a convertersection that receives three-phase line voltage for the line voltageinput and converts the three-phase line voltage to a single phase DCvoltage that charges the energy storage section.
 8. The ERT unit ofclaim 7, further comprising at least one charging contactor on the ERTcircuit between the converter section and the energy storage section,wherein the at least one charging contactor is movable between: an openposition, whereby the energy storage section is electricallydisconnected from the converter section; and a closed position, wherebythe energy storage section receives the single-phase DC voltage from theconverter section.
 9. The ERT unit of claim 8, comprising a dischargecontactor connected between the positive and negative lines of the ERTcircuit, wherein the discharge contactor is disposed between theconverter section and the energy storage section, and wherein thedischarge contactor is movable between: a closed position configured tocause the energy storage section to discharge stored energy, and an openposition, whereby the discharge contactor prevents the energy storagesection from discharging its stored energy on the ERT circuit.
 10. TheERT unit of claim 9, further comprising a resistor on the positive lineof the ERT circuit, the resistor connected in series with the dischargecontactor and the energy storage section.
 11. The ERT unit of claim 9,wherein the discharge contactor is normally closed, the at least onecharging contactor is normally open, and the output contactor isnormally open.
 12. An electrical drive system comprising: a drivecircuit having a positive line; and an electrical ride-through (ERT)unit configured to apply a voltage energy to the electrical drive systemduring a disruption of line voltage input to the drive circuit of theelectrical drive system, the ERT unit comprising: an ERT circuit havinga positive line and a negative line, the ERT circuit in a firstcondition being configured to selectively couple the positive line ofthe ERT circuit with the positive line of the drive circuit, the ERTcircuit in a second condition being configured to selectively decouplethe positive lines of the ERT circuit and the drive circuit; an energystorage section connected between the positive and negative lines of theERT circuit, the energy storage section configured to selectively storeand discharge energy, wherein a cathode of the energy storage section ofthe ERT unit is configured to be electrically connected to the positiveline of the drive circuit; and an output diode disposed on the positiveline of the ERT circuit, wherein in response to the ERT circuit in thefirst condition having the positive line of the ERT circuit coupled tothe positive line of the drive circuit, the output diode is: disposed inelectrical connection between the energy storage section and thepositive line of the drive circuit, configured to prevent electricalcurrent from flowing when a voltage level on the drive circuit isgreater than a voltage level of the energy storage section, andconfigured to permit electrical current to flow when the voltage levelon the drive circuit is less than the voltage level of the energystorage section.
 13. The electrical drive system of claim 12, whereinthe energy storage section is charged to a voltage less than a voltagethat is applied to a load on the drive circuit.
 14. A method ofproviding electrical power from an electrical ride-through (ERT) unit toa load on a drive circuit during a ride-through event, the methodcomprising the steps of: causing a three-phase line voltage to be inputto the drive circuit so as to drive the load at an operating voltage;and charging an ERT capacitor of an ERT circuit of the ERT unit tosubstantially a target voltage that is less than the operating voltage,the ERT capacitor connected between positive and negative lines of theERT circuit; selectively coupling the positive line of the ERT circuitin a first condition with a positive line of the drive circuit andselectively decoupling the positive line of the ERT circuit in a secondcondition with the positive line of the drive circuit; using a diodedisposed between the positive lines of the ERT circuit and the drivecircuit to prevent electrical current from flowing from the ERTcapacitor to the drive circuit in response to the target voltage beingless than a level of the operating voltage of the drive circuit; and inresponse to a voltage drop on the drive circuit making the level of theoperating voltage less than the target voltage, using the diode topermit electrical current to flow from the ERT capacitor to the drivecircuit.
 15. The method of claim 14, further comprising beginningoperation of the ERT unit in a charging mode, whereby a chargingcontactor disposed between a converter section of the ERT circuit andthe ERT capacitor is closed, and an output contactor disposed betweenthe ERT capacitor and the drive circuit is open.
 16. The method of claim15, further comprising iterating the ERT unit from the charging mode toa ride-through mode, whereby the output contactor is closed, and thecharging contactor is open.
 17. The method of claim 16, furthercomprising the step of iterating the ERT unit from the ride-through modeto the charging mode after electrical current has flowed from the ERTcapacitor to the drive circuit.
 18. The method of claim 16, furthercomprising the steps of: iterating the ERT unit from the ride-throughmode to a discharge mode whereby the output contactor is open, thecharging contactor is open, and a discharge contactor is closed; andpermitting energy to be discharged from the ERT capacitor to the ERTcircuit, wherein: the discharge contactor is connected between thepositive and negative lines of the ERT circuit, the discharge contactoris disposed between the converter section and the ERT capacitor, and thedischarge contactor is open in the charging mode and in the ride-throughmode.
 19. The method of claim 18, further comprising the step of causingelectrical current from the ERT capacitor to flow through a resistor asthe ERT capacitor is discharged.
 20. The method of claim 14, furthercomprising the step of powering auxiliary components of the drivecircuit with a generator on the ERT circuit during a disruption of linevoltage to the drive circuit.
 21. The ERT unit of claim 9, furthercomprising a controller configured to control the at least one chargingcontactor, the output contactor, and the discharge contactor to iteratethe ERT circuit between a charging mode, a ride-through mode, and adischarge mode; wherein the ERT unit in the charging mode has the atleast one charging contactor closed, the discharge contactor open, andthe output contactor open; wherein the ERT unit in the ride-through modehas the at least charging contactor open, the discharge contactor open,and the output contactor closed; and wherein the ERT unit in thedischarge mode has the at least one charging contactor open, thedischarge contactor closed, and the output contactor open.